WO2020225132A1

WO2020225132A1 - An electrical machine comprising a cooling device

Info

Publication number: WO2020225132A1
Application number: PCT/EP2020/062144
Authority: WO
Inventors: Peter Sergeant; Hendrik VANSOMPEL; Jasper NONNEMAN
Original assignee: Universiteit Gent
Priority date: 2019-05-08
Filing date: 2020-04-30
Publication date: 2020-11-12
Also published as: EP3966915A1

Abstract

A cooling device for cooling an electrical machine, the electrical machine comprising wound stator coils having end portions and axial portions, the cooling device comprising an annular heat collector arranged for engaging with an external heat sink, a plurality of coil receiving spaces each delimited by at least two radial extensions extending radially from the annular heat collector, the plurality of coil receiving spaces being arranged for receiving end portions of the plurality of wound stator coils, wherein the cooling device is made from a thermally conductive and non-ferromagnetic material, such that in use heat generated by the plurality of wound stator coils is conducted in a radial direction along the plurality of radial extensions and along the annular heat collector towards the external heat sink.

Description

AN ELECTRICAL MACHINE COMPRISING A COOLING DEVICE

Technical field

The invention relates to the technical field of electrical machines operable as an electrical generator or an electrical motor. The invention in particular relates to a cooling device for cooling wound stator coils, in particular for conducting heat from a plurality of wound stator coils of a stator of the electrical machine, to an external heat sink. In particular the invention relates to a cooling device for cooling wound stator coils of an electrical machine having concentrated windings.

State of the art

Most electrical machines generate heat when in use due to inevitable losses. A particular source of heat generation in electrical machines is the current carrying conductors provided in the stator of the electrical machine. In particular the coils wound around the stator teeth provided on the stator yoke of a stator of the electrical machine are an important source of heat generation. Such a wound stator coil comprises axial portions extending in the axial direction for example adjacent to axial portions of the stator teeth, for example adjacent to opposing axial portions of a stator tooth in an electrical machine with concentrated windings. Such a wound stator coil further comprises end portions i.e. rounded portions interconnecting the axial portions for example interconnecting axial portions at opposite sides of the stator tooth in an electrical machine with concentrated windings. The coils produce Joule heating due to the resistance to current flow in the windings of the coils (referred to as l²R losses). In order to avoid overheating of the electrical machine, in particular to avoid degradation of the electrical insulation coatings provided around the current carrying wires, it is primordial that the generated heat is transferred away from the coils towards an external heat sink. In conventional electrical machines, as shown in figure 1 , a substantial amount of the heat generated by the wound stator coils is transferred towards the stator core, i.e. the stator teeth and stator yoke. The external heat sink is arranged to subsequently transfer, for example dissipate, the heat from the stator core, into the environment surrounding the electrical machine. Different mechanisms of external heat sinks exist, wherein in general a cooling medium engages with the stator yoke, for example is brought into contact with the stator yoke. Examples of external heat sinks in an inner-rotor electrical machine are a thermally conductive sleeve with heat sink fins at its exterior and slid over the stator yoke as shown in figure 1 , or a water jacket such as a set of cooling-fluid-carrying cooling ducts in contact with the stator yoke, for example provided near a radially outward surface of the stator yoke, or a combination of the above. In case of outer rotor electrical machines, the external heat sink is for example a water jacket for example provided near a radially inward surface of the stator yoke or a thermally conductive sleeve in contact with the radially inward surface of the stator yoke, or a combination of the above. It has however been found that in electrical machines and in particular in so called electrical machines with concentrated windings, some portions of the wound stator coils, in particular end portions of the wound stator coils and outer windings of the wound stator coils, are located far away from the stator yoke and teeth, thereby limiting the removal of heat from these remote portions of the wound stator coil towards the external heat sink. Transfer of heat that is generated in the outer windings of the wound stator coils, i.e. the windings that are separated from the stator core by adjacent windings of the wound stator coil, for example has to be conducted through the isolation material provided on said adjacent windings of the wound stator coils, thereby limiting the removal of heat from these outer windings of the wound stator coil towards the external heat sink. Transfer of heat that is generated in the end portions of the wound stator coils, is additionally hindered by the lack of direct contact between the windings in the end portions, i.e. the inner winding in the end portion, and the stator teeth, due to the bending of the windings in the end portions around the stator teeth. Solutions have been provided in the state of the art to improve the removal of heat from the above mentioned‘remote portions’ of the wound stator coils. A first kind of solutions tend to improve the thermal conduction from the remote portions of the wound stator coil towards the stator core. One such solution is proposed in the patent publication EP0414507, where a triangular block is provided along an axial portion of the coils, for example between the axial portions of neighboring coils provided on neighboring stator teeth, such as to conduct away the heat that is generated in the outer windings of the wound stator coils towards the stator yoke. A further solution is proposed in the patent publication US20160285346, where the end portions of the wound stator coils are cooled using thermally conductive elements placed between the stator teeth and the coil end portions. The heat is thereby removed from the remote portions of the wound stator coils and transferred to the stator teeth for further removal. It has however been found that the state of the art cooling devices for cooling remote portions of the wound stator coils, in particular the end portions of the wound stator coils, do not sufficiently remove the heat of the wound stator coils. A second kind of solutions, as proposed in patent publication BE1015432 tends to cool the‘remote portions’ by spraying coolant onto the remote portions. It has however been found that this solution does not sufficiently remove the heat of the wound stator coils. It has furthermore been found that this solution requires providing complex and thus expensive coolant circulating circuits.

Description of the invention

It is an object of the present invention to provide a cooling device for in use conducting heat from a plurality of wound stator coils of a stator, in particular from remote portions of the wound stator coil, in particular from end portions of the stator coils, towards an external heat sink, wherein the problem of the state of the art is solved. The present invention therefore provides a cooling device according to the first claim. The cooling device is arranged for cooling an electrical machine. The electrical machine for example comprises a stator having a stator yoke and a plurality of radially extending stator teeth provided on the stator yoke. The electrical machine for example further comprises a rotor positioned co-axially with the stator, for example such as to form a motor or a generator. The electrical machine comprises a plurality of wound stator coils comprising end portions and axial portions, wherein each wound stator coil is for example wound around at least one of the plurality of stator teeth, preferably around one of the plurality of stator teeth such as to create an electrical machine with concentrated windings. The cooling device of the present invention comprises an annular heat collector, i.e. an annulus, for example a ring shaped element, configured for collecting heat. Preferably, the annular heat collector forms a hollow cylinder. Throughout the present description reference is made to a cylindrical coordinate system for example defined by the annular heat collector, namely having a circumferential direction following the annular periphery of the annular heat collector, a corresponding radial direction and a corresponding axial direction. The annular heat collector is arranged for engaging with the external heat sink i.e. for in use being in thermally conductive arrangement with the external heat sink, for example being in direct contact with the external heat sink. The cooling device comprises a plurality of coil receiving spaces each delimited by at least two radial extensions extending radially from the annular heat collector, i.e. forming a plurality of radially extending teeth. The plurality of coil receiving spaces are arranged for, in use, receiving end portions of the plurality of wound stator coils, for example in an electrical machine with concentrated windings each coil receiving space is arranged for in use receiving an end portion, i.e. a single end portion, of a wound stator coil. The at least two radial extensions of a coil receiving space are thus arranged for, in use, receiving an end portion of a wound stator coil, i.e. for receiving an end portion of a wound stator coil between them. The coil receiving space may thus be defined as a space between the at least two radial extensions of the cooling device. Thereto, the at least two radial extensions of a coil receiving space may each extend radially from the annular heat collector and may be separated from each other along the axial direction, thereby forming a space between them for receiving an end portion of a wound stator coil, i.e. thereby forming the coil receiving space. The plurality of radial extensions delimiting the coil receiving spaces are preferably arranged for, in use, contacting end portions of the plurality of wound stator coils. Contacting between the cooling device and the wound stator coils, for example contacting between the radial extensions of the cooling device and the end portions of the wound stator coils, may be defined as thermal contacting. It will be understood by a person skilled in the art that an additional electrical insulating liner may be provided between the cooling device and the wound stator coil in order to prevent a short-circuit current from being generated in the cooling device when voltage is applied to the wound stator coils. Alternatively, the cooling device, and in particular the parts of the cooling device in contact with the wound stator coil, may comprise or be made from an electrical insulating material, avoiding the need for an additional electrical insulating liner or layer. Concluding, contacting between the cooling device and the wound stator coils, for example contacting between the radial extensions of the cooling device and the end portions of the wound stator coils, may comprise both direct contacting as indirect contacting, whereby indirect contacting comprises providing an additional electrical insulating layer between the cooling device and the wound stator coils.

The cooling device, in particular the annular heat collector and the plurality of radial extensions, is made from a thermally conductive and non-ferromagnetic material, such that in use heat generated by the plurality of wound stator coils, in particular generated by the remote portions such as the end portions of the wound stator coils, is conducted in a radial direction along the plurality of radial extensions and along the annular heat collector towards the external heat sink, which is in use engaged with the annular heat collector.

The cooling device of the present invention overcomes the problem of insufficient heat removal from the remote portions of the wound stator coil, as is encountered in cooling devices of the state of the art, in particular as disclosed in US20160285346. The thermally conductive radial extensions of the present invention being disposed in a radially extending configuration, facilitate the transfer of heat from the end portions of the wound stator coil towards the annular heat collector. The annular heat collector, being an annulus, provides a large volume for collecting the heat, and provides a large contact area for engaging with the external heat sink. The heat is thus conducted radially through the radially extending radial extensions, and subsequently radially through the annulus towards the external heat sink. Upon leaving the radial extensions, the heat is spread over the large area of the annular heat collector which spans 360°, thus facilitating the radial heat transport. As an example, without limiting the invention, the external heat sink is for example a thermally conductive sleeve with heat sink fins at its exterior, that is slid over and rests on the stator yoke and the annular heat collector. In the example, the heat is radially conducted across the annular heat collector up to the surface whereon the external heat sink rests.

A further advantage of the cooling device of the present invention is that the electrical device can be easily assembled. The mounting of the cooling device onto the stator requires a limited amount of actions. In particular the cooling device of the present invention does not need separate mounting of cooling elements per stator teeth as is required in the cooling devices of the state of the art. To the contrary, in a single action, a single cooling device can be mounted onto the stator covering all the stator teeth. A further advantage of the cooling device of the present invention is that conventional external heat sinks can be used with minor adaptations. In particular in certain embodiments of the present invention, is suffices to extend the conventional external heat sink used for cooling the stator core in conventional electrical machines, as is shown in figure 1 , such as to axially extend beyond the stator core and up to the cooling device of the present invention. As an example, without limiting the invention, a conventional external heat sink comprising a thermally conductive sleeve to be slid over and rest on the stator yoke, can be extended in the axial direction, i.e. made longer. The extended conventional external heat sink is then simultaneously slid over and resting on both the stator yoke and the annular heat collector. The axially extended external heat sink can simply be manufactured prior to the assembly, thereby not altering the subsequent conventional mounting/assembly process for electrical machines.

Because the cooling device is made of a non-ferromagnetic material, the amount of magnetic flux going through the cooling device is drastically limited, for example substantially limited to leakage and fringing magnetic fluxes. This has the advantage that the magnetic flux can be concentrated towards the rotor of the electrical machine, i.e. the path of the magnetic flux is substantially similar to the path of the magnetic flux in an electrical machine that is not provided with the cooling device of the present invention.

Radial extensions are for example radially extending tabs, for example plates, provided on the annular heat collector.

In embodiments of the present invention, the at least two radial extensions comprise a first radial extension for, in use, contacting inner windings of an end portion of the wound stator coil, and a second radial extension for, in use, contacting outer windings of an end portion of the wound stator coil. Inner windings of an end portion of a wound stator coil are defined as part of the turns or windings constituting the stator coil that have in the end portion an axial position closest to the stator tooth. Outer windings of an end portion of a wound stator coil are defined as part of the turns or windings constituting the stator coil that have in the end portion an axial position furthest away from the stator tooth. In embodiments of the present invention, the first radial extension is arranged such that in use heat generated from inner windings of the end portions of the wound stator coils is conducted in a radial direction along the first radial extension and along the annular heat collector towards the external heat sink and the second radial extension is arranged such that in use heat generated from outer winding of the end portions of the wound stator coils is conducted in a radial direction along the second radial extension and along the annular heat collector towards the external heat sink.

In embodiments of the present invention the at least two radial extensions comprise a first radial extension comprising a tooth engaging surface, engaging with , for example contacting with, a surface of the stator tooth, and a second radial extension comprising a coil engaging surface engaging with, for example contacting with, a surface of the wound stator coil, for example contacting with a surface of the outer windings of the wound stator coil.

In an embodiment of the present invention the thermally conductive and non ferromagnetic material of the cooling device has a relative permeability substantially equal to 1. The embodiment has the advantage that the amount of magnetic flux in the cooling device is drastically reduced, for example substantially limited to leakage and fringing magnetic fluxes. Reducing the magnetic flux paths through the cooling device has the advantage of reducing the energy loss due to the development of induced eddy currents within the cooling device.

In an embodiment of the present invention the plurality of radial extensions are slotted in the radial direction such as to in use limit the formation of induced eddy currents. By providing the slotting in the radial direction, the heat can be easily transferred in the radial direction via the radial extensions towards the annular heat collector without being hindered by the slots. The term slotting comprises segmenting the radial extension into different parts extending in the radial direction, for example comprising an alternation of parts of relatively high electrical conductivity material such as the thermally conductive and non-ferromagnetic material of the cooling device, on the one hand and parts of low electrically conductive material such as air on the other hand. The slotted radial extensions are for example referred to as a slotted structure, a comb structure or a fingered structure. The slots are preferably slotted planes extending in the radial direction. The slotted planes are preferably perpendicular to the circumferential direction of the cooling device. According to a further embodiment of the present invention at least a part of the annular heat collector is provided with a slotted structure, preferably slotted in the radial direction, for example extending the slotted structure of the plurality of radial extensions.

In an embodiment of the present invention, the thermal conductivity of the thermally conductive and non-ferromagnetic material of the cooling device is superior to the thermal conductivity of the stator core, in particular the stator yoke and stator teeth. It has namely been found that the thermal conductivity of conventional stator cores, i.e. the stator teeth and the stator yoke, are limited, for example to around 30 Wm- 1 K-1 . The stator core therefore insufficiently removes heat away from the current carrying windings of the coil. By consequence, the stator core also insufficiently removes heat away from the cooling devices of the cited state of the art, as these cooling devices strongly rely on the transfer of heat to the external heat sink via the stator core. In the cooling device of the present invention, the thermally conductive cooling device is itself engaged with the external heat sink, such that it relies to a lesser degree on the transfer of heat via the stator core. In a preferred embodiment of the present invention the thermal conductivity of the thermally conductive and non-ferromagnetic material of the cooling device is above 30 Wm- 1 K-1 , by preference above 100 Wm-1 K-1 . The increased thermal conductivity of the cooling device ensures that sufficient heat is conducted away from the wound stator coils towards the external heat sink through the radial extensions and the annular heat collector.

According to an embodiment of the present invention, the annular heat collector comprises a first annular part and a second annular part, and wherein the first annular part and the second annular part are separate and connectable parts. According to another embodiment of the present invention, the annular heat collector comprises a first annular part and a second annular part, and wherein the first annular part and the second annular part are integrally connected parts. Preferably, openings in the first annular part and second annular part provide for the coil receiving space within the annular heat collector.

According to an embodiment of the present invention, the annular heat collector is divided into multiple circumferential sections each spanning an arc of less than 360°, wherein each circumferential section of the annular heat collector is provided with a coil receiving space. By preference, the amount of circumferential sections of the annular heat collector equals the amount of stator teeth, in particular in embodiments wherein one wound stator coil is provided on each stator tooth such as in electrical machines with concentrated windings. By preference, each circumferential section of the annular heat collector spans an equal arc of less than 360°. By preference, the stator teeth divide the stator yoke into multiple circumferential sections each spanning a, preferably equal, arc of less than 360°, wherein the multiple circumferential sections of the annular heat collector correspond to the circumferential sections of the stator yoke. In a first implementation, the circumferential sections of the annular heat collector are separate and interconnectable components. In this implementation the separate circumferential sections of the annular heat collector can be interconnected, i.e. assembled, such as to span the entire 360°. The separate circumferential sections are preferably provided with mechanical interlocking members, for example female and/or male members arranged to interlock with corresponding mechanical interlocking members of adjacent circumferential sections. In an alternative implementation, the circumferential sections of the annular heat collector are integrally connected, i.e. are not separate and interconnectable.

It is a further object of the present invention to provide an electrical machine comprising the cooling device for cooling the electrical machine. The electrical machine comprises

• a stator having a stator yoke, a plurality of radially extending stator teeth provided on the stator yoke, and a plurality of wound stator coils comprising end portions and axial portions, wherein for example each wound stator coil is wound around at least one of the plurality of stator teeth, for example around a single one of the plurality of stator teeth in an electrical machine with concentrated windings,

• an external heat sink engaging with the stator yoke, for example in direct contact with the stator yoke and/or fitted to the stator yoke, for removing heat from the electrical machine, and

• the cooling device as explained above, for in use conducting heat from the plurality of wound stator coils, in particular from remote portions of the wound stator coil such as from end portions of the wound stator coil, to the external heat sink. The annular heat collector engages with the external heat sink. The annular heat collector is for example in direct contact with the external heat sink. The plurality of coil receiving spaces receive end portions of the plurality of wound stator coils, for example in electrical machines with concentrated windings each coil receiving space receives a single end portion of a single one of the plurality of wound stator coils. In use, heat generated by the plurality of wound stator coils, in particular by remote portions of the wound stator coils such as the end portions of the wound stator coils, is conducted in a radial direction along the plurality of radial extensions and along the annular heat collector towards the external heat sink.

According to an embodiment of the present invention the stator yoke extends in an axial direction. Preferably, the stator yoke forms a hollow cylinder. Preferably, the stator yoke has a circumferential direction along its annular periphery, and a corresponding axial direction and radial direction. Preferably, in use, the axial direction of the stator yoke is the same direction as the axial direction of the annular heat collector. The stator yoke is delimited by a radially inward surface, a radially outward surface and two axially opposed end surfaces each interconnecting the radially inward surface and the radially outward surface. Preferably the electrical machine comprises a rotor arranged co-axially with the stator core, for example within the stator core or surrounding the stator core such as to respectively create an inner-rotor or outer-rotor electrical machine. The rotor for example cooperates with the stator such as to form a motor or a generator. The cooling device is for example arranged to cool the motor or generator. Preferably, the plurality of radially extending stator teeth are provided on a rotor-facing surface of the stator yoke, i.e. a surface facing the rotor, the rotor-facing surface being at least one of, preferably merely one of, the radially inward surface or radially outward surface of the stator yoke, such as to respectively create an inner-rotor electrical machine or an outer- rotor electrical machine. The stator teeth preferably divide the stator yoke into multiple circumferential sections each spanning a, preferably equal, arc of less than 360°, preferably corresponding to the circumferential sections of the annular heat collector. The stator teeth are delimited by opposing axial portions and opposing end portions each interconnecting the opposing axial portions. The axial portions of the stator teeth are preferably tooth surfaces that are perpendicular to the circumferential direction of the stator yoke and that substantially extend in the axial direction, preferably between two axial end surfaces of the stator yoke. The end portions are preferably tooth surfaces that are perpendicular to the axial direction of the stator yoke. Each wound stator coil has axial portions extending along the axial portions of the stator teeth. Preferably in so called electrical machines with concentrated windings, each wound stator coil has opposing axial portions extending along opposing axial portions of one of the stator teeth. Each wound stator coil has end portions extending around the end portions of the stator teeth, for example such as to interconnect the axial portions of the wound stator coil. Preferably in so called electrical machines with concentrated windings, each wound stator coil has opposing end portions extending around the opposing end portions of one of the stator teeth. According to a preferred embodiment of the present invention, the electrical machine is an electrical machine with concentrated windings, as opposed to an electrical machine with distributed windings. Preferably, in wound stator coils with concentrated windings, every single wound stator coil comprises multiple turns of windings concentrated around a single stator tooth. The wound stator coil comprising concentrated windings has opposing axial portions lying adjacent to opposing axial portions of a single stator tooth and has opposing end portions interconnecting its opposing axial portions.

According to an embodiment of the present invention, the annular heat collector of the cooling device is delimited by a radially inward surface, a radially outward surface and two axially opposed end surfaces each interconnecting the radially inward surface and the radially outward surface. The plurality of radially extending radial extensions are provided on a rotor-facing surface of the annular heat collector i.e. a surface facing the rotor, the rotor-facing surface being at least one of, preferably merely one of, the radially inward surface or radially outward surface of the annular heat collector.

According to an embodiment of the present invention, the cooling device is mounted on the stator, for example attached to the stator, such that one of the end surfaces of the annular heat collector, called the stator facing surface, lies parallel with, and adjacent to, one of the end surfaces of the stator yoke. Preferably the stator facing surface of the annular heat collector is in contact with one of the end surfaces of the stator yoke. According to an embodiment of the present invention, the electrical machine comprises a second cooling device mounted on the stator, for example attached to the stator, such that the stator facing surface of the annular heat collector of the second cooling device lies parallel with, and adjacent to the end surface of the stator yoke opposing the end surface of the stator yoke on which the first cooling device is mounted.

According to an embodiment of the present invention, the electrical machine is an outer-rotor electrical machine. According to another embodiment of the present invention the electrical machine is an inner-rotor electrical machine. According to an embodiment of the present invention, the electrical machine has both an inner- rotor and an outer-rotor, i.e. is a dual rotor electrical machine. According to an embodiment of the present invention, the plurality of radially extending stator teeth are extending respectively radially outward from the outer radial surface of the stator yoke or radially inward from the inner radial surface of the stator yoke, such as to form respectively the outer-rotor electrical machine or the inner-rotor electrical machine. The plurality of radial extensions are extending respectively radially outward from the outer radial surface of the annular heat collector or radially inward from the radially inward surface of the annular heat collector such as to form respectively the outer-rotor electrical machine or the inner-rotor electrical machine. In embodiments were the electrical machine is a dual rotor electrical machine, the plurality of radially extending stator teeth and the plurality of radial extensions are both extending radially inward and radially outward.

According to an embodiment of the present invention, the stator yoke and the annular heat collector comprise a set of openings extending substantially in the axial direction, and the external heat sink comprises a plurality of cooling ducts formed by the set of openings, wherein the cooling ducts are arranged to in use extract heat from the stator yoke and the annular heat collector by flowing a heat transfer fluid through the cooling ducts. In the present embodiment the external heat sink is a fluid jacket, for example a water jacket. Preferably, the openings in the set of openings provided in the stator yoke are co-axial with the openings in the set of openings provided in the annular heat collector, such that a straight cooling duct is formed. Preferably, the cooling ducts are formed by inserting a fluid carrying tube through each opening of the set of openings. The present embodiment is particularly advantageous in dual rotor electrical machines.

According to an embodiment of the present invention, preferably where the electrical machine is not a dual rotor electrical machine, the external heat sink comprises a thermally conductive sleeve in contact with the surface opposed to the rotor-facing surface. The thermally conductive sleeve is preferably provided with heat sink fins at its exterior surface and/or cooling ducts within the sleeve, such as to facilitate the transfer, for example the dissipation, of heat to the surroundings of the electrical machine. Preferably, the thermally conductive sleeve has a thermal conductivity superior to the thermal conductivity of the stator core. Preferably the thermally conductive sleeve is made from a material with a thermal conductivity superior to 30 Wm-1 K-1 , by preference above 100 Wm-1 K-1 . By preference, the thermally conductive material of the thermally conductive material is a non-ferromagnetic material, preferably having a relative permeability substantially equal to 1 . By preference, the thermally conductive material of the thermally conductive sleeve is the same material as the thermally conductive and non-ferromagnetic material of the cooling device. According to a first implementation, the external heat sink comprises the thermally conductive sleeve in contact with both the surface opposed to the rotor-facing surface of the stator yoke and the surface opposed to the rotor-facing surface of the annular heat collector. This implementation ensures that the external heat sink optimally extracts heat from both the stator core and the cooling device. Preferably the surface opposed to the rotor-facing surface of the stator yoke and the surface opposed to the rotor-facing surface of the annular heat collector lie substantially flush. The surfaces lie substantially flush when they lie substantially level or even with each other. In one example, the surfaces lay in each other’s axial extension, in particular one of the surfaces is not substantially indented or protruding in the radial direction with respect to the other surface, i.e. when the radial indentation or protrusion are merely caused by machine inaccuracies. This has the advantage that a conventional thermally conductive sleeve, that is slightly lengthened along the axial direction, can be used. This furthermore has the advantage that the thermally conductive sleeve can be easily slid in place. In another example, the surface opposed to the rotor-facing surface of the stator yoke and the surface opposed to the rotor-facing surface of the annular heat collector lie parallel to each other, and one of the surfaces is slightly protruding in the radial direction with respect to the other surface, e.g. the cylinder of the stator yoke and the cooling device might have a small difference in diameter as to incorporate a“small” step in the combined cylindrical surface. This step in diameter then can be used in production to guarantee a correct positioning of the thermally conductive sleeve of the external heat sink with respect to the stator yoke and cooling device. Such configuration is also defined as substantially flush. Preferably, the external heat sink of the first implementation additionally comprises cooling ducts provided through the stator yoke and the annular heat collector as in the preceding embodiment. According to a second implementation the thermally conductive sleeve and the annular heat collector comprise a set of openings extending in the axial direction, and the external heat sink comprises a plurality of cooling ducts formed by the set of openings, wherein the cooling ducts are arranged to in use extract heat from the thermally conductive sleeve and the annular heat collector by flowing a heat transfer fluid through the cooling ducts. Preferably, the openings in the set of openings provided in the thermally conductive sleeve are co-axial with the openings in the set of openings provided in the annular heat collector, such that a straight cooling duct is formed. Preferably, the cooling ducts are formed by inserting a fluid carrying tube through each opening of the set of openings.

According to an embodiment of the present invention, each coil receiving space is further delimited by the rotor-facing surface of the annular heat collector. The cooling device according to the present embodiment comprises a plurality of coil receiving spaces each delimited by at least one radial extension and the rotor facing surface of the annular heat collector, such that the end portions of the wound stator coils that are received in the coil receiving spaces are in contact with multiple cooling surfaces, i.e. at least one coil engaging surface of the radial extension and the rotor-facing surface of the annular heat collector. To implement the present embodiment, the annular heat collector preferably has a width in the axial direction which is superior to the width in the axial direction of the at least one radial extension, in particular of one of the teeth engaging radial extension or coil engaging radial extension as will be described further below.

According to an embodiment of the present invention, the annular heat collector comprises a first annular part and a second annular part. Preferably the first annular part comprises the stator facing surface and the second annular part comprises the end surface of annular heat collector opposing the stator facing surface, referred to as the surrounding-facing end surface. Preferably, each annular part is an annulus i.e. a ring-shaped element. Preferably the first annular part and the second annular part are co-axial. In a first implementation the first annular part and the second annular part are separate and connectable parts. In the first implementation, the first annular part and the second annular part are connected to each other, for example by positioning both annular parts co-axially and by connecting them to each other, for example via a mechanical interlocking mechanism. In a second implementation, the first annular part and the second annular part are integrally connected parts, i.e. not separate and connectable parts.

According to an embodiment of the present invention, one of the at least one radial extension delimiting each coil receiving space is a tooth engaging radial extension extending radially from the rotor-facing surface of the annular heat collector. The tooth engaging radial extension is preferably a tab, i.e. a plate, with a major plane perpendicular to the axial direction. The tooth engaging radial extension extends from the annular heat collector from a position adjacent the stator facing surface of the annular heat collector, towards a free end. The tooth engaging radial extension is delimited by a tooth engaging surface, an opposite coil engaging surface and two sidewalls each interconnecting the tooth engaging surface and the coil engaging surface. The two sidewalls of the tooth engaging surface for example allow the passage of the axial portions of the wound stator coil into the coil receiving space. The tooth engaging radial extension simultaneously contacts one of the end portions of the stator tooth with the tooth engaging surface and one of the corresponding end portions of the wound stator coil, in particular the inner windings of the end portion, with the coil engaging surface. Because the tooth engaging radial extension is anchored to the annular heat collector at a position adjacent to the stator facing surface of the annular heat collector, the tooth engaging radial extension will be provided on the first annular part of the annular heat collector. The present embodiment has the advantage that heat is easily extracted from the inner windings of the end portions of the wound stator coils and is easily conducted towards the external heat sink via the radial extension. Preferably, the tooth engaging surface of the tooth engaging radial extension is planar, such as to conform to the planar shape of the end portions of the stator teeth. Preferably, the coil engaging surface of the tooth engaging insert is substantially C-shaped and bulges away from the tooth engaging surface, i.e. is convex, such as to conform to the bended shape of the end portions of the wound stator coils.

According to an embodiment of the present invention, one of the at least one radial extension delimiting each coil receiving space, is a coil engaging radial extension extending radially from the rotor-facing surface of the annular heat collector. The coil engaging radial extension is preferably a tab, i.e. a plate, with a major plane perpendicular to the axial direction. The coil engaging radial extension extends from the annular heat collector from a position adjacent the end surface opposite to the stator facing surface of the annular heat collector, towards a free end. The coil engaging radial extension is delimited by a coil engaging surface in contact with one of the end portions of the wound stator coil, in particular with outer windings of the end portion of the wound stator coil, by preference the outer windings that run substantially in the circumferential direction of the cooling device. The coil engaging radial extension is preferably further delimited by a surrounding facing surface opposed to the coil engaging surface. Because the coil engaging radial extension is anchored to the annular heat collector at a position adjacent to the surrounding-facing end surface of the annular heat collector, the coil engaging radial extension will be provided on the second annular part of the annular heat collector. The present embodiment has the advantage that heat is easily extracted from the outer windings of the end portions of the wound stator coils and is easily conducted towards the external heat sink via the radial extension. Preferably, the coil engaging surface of the coil engaging radial extension is substantially C- shaped and bulges towards the surrounding-facing surface of the coil engaging radial extension, i.e. is concave, such as to conform to the bended shape of the end portions of the wound stator coils. According to an embodiment of the present invention, each coil receiving space is delimited by at least the coil engaging surface of the coil engaging radial extension, the coil engaging surface of the tooth engaging radial extension, and the rotor-facing surface of the annular heat collector.

According to an embodiment of the present invention, preferably where the electrical machine has wound stator coils with concentrated windings, one of the at least one radial extension delimiting each coil receiving space is a side engaging radial extension extending radially from the rotor-facing surface of the annular heat collector. Preferably, each coil receiving space is delimited by two side engaging radial extensions. The side engaging radial extension is preferably a tab, i.e. a plate, with a major plane perpendicular to the circumferential direction, i.e. the side engaging radial extension is connected to the annular heat collector over substantially the entire axial width of the annular heat collector for example split across the first and second annular parts of the annular heat collector. The side engaging radial extension extends from the annular heat collector, towards a free end. The side engaging radial extension is delimited by a coil engaging surface in contact with one of the end portions of the stator tooth, in particular with outer windings of the end portion of the wound stator coil, by preference the outer windings that run substantially in the axial direction of the cooling device. The present embodiment has the advantage that heat is easily extracted from the outer windings of the end portions of the wound stator coils and is easily conducted towards the external heat sink via the radial extension. According to an embodiment of the present invention, each coil receiving space is delimited by at least the coil engaging surface of the coil engaging radial extension, the coil engaging surface of the tooth engaging radial extension, the coil engaging surfaces of two opposed side engaging radial extensions and the rotor-facing surface of the annular heat collector. Preferably, the space between the side engaging radial extensions of neighboring coil receiving spaces is filled with the thermally conductive and non-ferromagnetic material of the cooling device such as to form a raised portion on the annular heat collector with a substantially triangular cross- section in a plane perpendicular to the axial direction.

According to an embodiment of the present invention, preferably where the electrical machine has wound stator coils with concentrated windings, the cooling device comprises a plurality of axial extensions. Preferably, the plurality of axial extensions are integrally connected to the annular heat collector, preferably to the first annular part of the annular heat collector. Preferably, the annular heat collector is provided with the raised portions presented above, wherein the axial extensions are integrally connected to the raised portions. Preferably, the axial extensions are provided between adjacent tooth engaging radial extensions. Preferably each circumferential section of the annular heat collector is provided with a pair of axial extensions, preferably provided at circumferentially opposite sides of the circumferential section. The axial extensions axially extend into the stator, preferably into the space between two adjacent stator teeth. The axial extensions are in contact with the axial portions of the wound stator coils, i.e. the axial portions of the wound stator coils are received between an axial extension and an axial portion of a stator tooth. In use, the axial extensions extract heat from the axial portions of the wound stator coil, in particular from the outer windings of the axial portions of the wound stator coil. The extracted heat is thermally conducted in the axial direction towards the annular heat collector. Preferably, the axial extensions are slotted such as to reduce to development of eddy currents. Preferably, the slots extend in the axial direction such as to allow thermal conduction of heat across the axial extension towards the annular heat collector. When two cooling devices are mounted on the opposite axial end surfaces of the stator yoke, the axial extensions of the two cooling devices preferably do not contact each other, i.e. an air gap is provided between the axial extensions of the opposing cooling devices, such as to further reduce the development of eddy currents.

According to an embodiment of the present invention, the cooling device comprises a main mounting unit. The main mounting unit preferably comprises at least the first annular part of the annular heat collector. The main mounting unit is arranged to enable mounting of the wound stator coil in wound state on to the stator tooth after mounting of main mounting unit on to the stator. The wound stator coil in wound state is a pre-wound stator coil, i.e. wound prior to mounting the stator coil onto the stator teeth. Preferably, the pre-wound stator coils are concentrated windings, as opposed to distributed windings. According to the present embodiment, the main mounting unit enables radial insertion of the pre-wound stator coil into the coil receiving space after having mounted the main mounting unit to the stator. The coil receiving spaces of the main mounting unit are therefore provided with a radial opening, for example an opening between the free ends of the radial extensions. The present embodiment therefore enables to provide an electrical machine with a cooling device wherein the mounting/assembly process is substantially simplified. Once the main mounting unit of the cooling device has been mounted to the electrical machine, for example such that the stator facing surface of the annular heat collector contacts an end surface of the stator yoke, and for example such that the tooth engaging surface of the tooth engaging radial extension contacts one of the end portions of the stator tooth, the wound stator coil in pre-wound state can be mounted onto the stator tooth in a conventional manner, in particular by inserting the wound stator coil into the space between the stator and the rotor and by simply lowering the pre-wound stator coil onto the stator tooth and for example onto the tooth engaging radial extension. The assembly/mounting of the present electrical machine requires no additional steps after placement of the main mounting unit. For example by providing an enlarged pre-wound stator coil, the pre-wound stator coil can simply be lowered onto the stator tooth and for example over the tooth engaging radial extension. The axial dimension of the enlarged pre-wound stator coil is thereto chosen to correspond to the summation of the axial dimension of the stator tooth and the tooth engaging axial extension or extensions if two cooling devices are mounted on the stator. Therefore, it is not required to perform the additional step of enlarging the pre-wound stator coil, for example by stretching the coil in the axial dimension whilst lowering it over the stator tooth and for example the tooth engaging radial extension(s).

According to an embodiment of the present invention, the cooling device comprises a further mounting unit, called the auxiliary mounting unit. The auxiliary mounting unit comprises a covering plate extending axially substantially parallel to the rotor facing surface of the annular heat collector. The covering plate, when mounted onto the main mounting unit, preferably contacts at least one, for example all of the free ends of the radial extensions delimiting the coil receiving space. The covering plate is delimited by a coil engaging surface arranged to contact one of the end portions of the wound stator coil, i.e. equivalently to the contact between the rotor facing surface of the annular heat collector and the end portion of the wound stator coil. Preferably, each coil receiving space is further delimited by its own separate covering plate. The auxiliary mounting unit is mountable to the main mounting unit, for example via a mechanical interlocking mechanism or for example by merely bringing the auxiliary mounting unit in contact with the main mounting unit. The wound stator coil in wound state, i.e. the pre-wound stator coil, is only mountable on to the stator tooth, and in particular on to the main mounting unit mounted on the stator, prior to connecting the auxiliary mounting unit with the main mounting unit. With‘only mountable’ is preferably not only meant that the mounting of the pre-wound stator coil would otherwise be physically impossible, but also for example that the mounting of the pre-wound stator coil would otherwise require additional steps such as the substantial axial stretching of the pre-wound stator coil. In one implementation, the first and second annular parts are separate and connectable parts, and the covering plate is integrally connected to at least one of the free ends of the radial extensions provided on the second annular part. The covering plate is for example integrally connected to the free ends of the coil engaging radial extensions of each coil receiving space. In this example, the second annular part comprising the coil engaging radial extensions and the covering plates, together form the auxiliary mounting unit, whilst the first annular part, for example provided with the tooth engaging radial extension forms the main mounting unit.

Figures

Figure 1 shows an electrical machine comprising a stator and an external heat sink according to the prior art.

Figure 2 shows an electrical machine comprising a stator and a cooling device according to an embodiment of the present invention.

Figures 3 and 4 show an exploded view of electrical machines according to an embodiment of the present invention, wherein two exemplary embodiments of the cooling device are displayed. Figure 3 in particular shows the cooling device comprising separate first and second annular parts. Figure 4 in particular shows the cooling device comprising integrally connected first and second annular parts.

Figures 5a-5b show an inner-rotor electrical machine according to an embodiment of the present invention wherein different external heat sinks are provided.

Figures 5c-5d show an outer-rotor electrical machine according to an embodiment of the present invention wherein different external heat sinks are provided.

Figure 6 shows an electrical machine according to an embodiment of the present invention wherein the cooling device comprises multiple intermediate radial extensions.

Figures 7 shows in detail a single circumferential section of the cooling device. Figure 8 shows a single circumferential section of the stator mounted with a single wound stator coil and two circumferential sections of an exemplary embodiment of the cooling device mounted on the stator.

Figure 9 shows two circumferential sections of an exemplary embodiment of the cooling device comprising a first part and a second overmold part.

Description of the figures

The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

Furthermore, the various embodiments, although referred to as“preferred” are to be construed as exemplary manners in which the invention may be implemented rather than as limiting the scope of the invention.

The term“comprising”, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising A and B” should not be limited to devices consisting only of components A and B, rather with respect to the present invention, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components. Figure 1 shows a conventional electrical machine 2 comprising a stator 3 and an external heat sink 9 according to the prior art. The rotor has not been drawn for clarity reasons. The conventional electrical machine 2 as shown in figure 1 is an inner-rotor electrical machine, wherein the rotor is positioned co-axially within the stator. The stator 3 of the prior art comprises a stator yoke 4, provided with a plurality of stator teeth 5. The stator teeth 5 comprise axial portions 1 1 extending in the axial direction and end portions 10 interconnecting the axial portions 1 1 . The axial portions 1 1 of the stator teeth 5 are the surfaces of the stator teeth 5 having a normal substantially parallel to the circumferential direction. The end portions 10 of the stator teeth 5 are the surfaces of the stator teeth 5 having a normal substantially parallel to the axial direction. A wound stator coil 6 is wound around each stator tooth 5, such as to form a stator 3 with concentrated windings. The wound stator coils 6 comprise opposing axial portions 8 adjacent the opposing axial portions 1 1 of the stator teeth 5. An axial portions 8 of the wound stator coil 6 is the bundle of current carrying wires extending substantially in the axial direction. The axial portions 8 of the wound stator coil are delimited by opposing surfaces having a normal substantially parallel to the circumferential direction. One of the opposing surfaces is formed by current carrying wires referred to as inner windings, and the other one of the opposing surfaces is formed by current carrying wires referred to as outer windings. The surface of the wound stator coil 6 axial portion 8 that comprises the inner windings lies adjacent, for example in contact with, an end portion 1 1 of a stator tooth 5. The wound stator coils 6 further comprise end portions 7 bending around the end portions 10 of the stator teeth 5 such as to interconnect the opposing axial portions 8 of the wound stator coil 6. The end portions 7 of the wound stator coil 6 is the bundle of current carrying wires interconnecting the axial portions 8 of the wound stator coil 6. The conventional electrical machine 2 is cooled by engaging an external heat sink 9 with the stator yoke 4. The external heat sink 9 as shown in figure 1 comprises a thermally conductive sleeve 9 slid over the stator yoke 4, i.e. resting on an outer radial surface of the stator yoke 4.

Figure 2 shows a cross-sectional view of an electrical machine 2 comprising a stator 3 and cooling devices 1 a and 1 b according to one embodiment of the present invention. For clarity reasons, the rotor and the external heat sink 9 are not shown. The electrical machine 2 as shown in figure 2 is an inner-rotor electrical machine wherein the rotor is positioned co-axially within the stator 3. The electrical machine 2 comprises a stator 3 having a stator yoke 4 and a plurality of radially extending stator teeth 5 provided on the stator yoke 4. The stator teeth 5 comprise axial portions 1 1 extending in the axial direction and end portions 10 interconnecting the axial portions 1 1 . The axial portions 1 1 of the stator teeth 5 are the surfaces of the stator teeth 5 having a normal substantially parallel to the circumferential direction. The end portions 10 of the stator teeth 5 are the surfaces of the stator teeth 5 having a normal substantially parallel to the axial direction. A wound stator coil 6 is wound around each stator tooth 5, such as to form a stator 3 with concentrated windings. The wound stator coils 6 comprise opposing axial portions 8 adjacent to the opposing axial portions 1 1 of the stator teeth 5. Axial portions 8 of the wound stator coil 6 is the bundle of current carrying wires extending substantially in the axial direction. The axial portions 8 of the wound stator coil are delimited by opposing surfaces having a normal substantially parallel to the circumferential direction. One of the opposing surfaces is formed by current carrying wires referred to as inner windings, closest to the stator tooth 5, and the other one of the opposing surfaces is formed by current carrying wires referred to as outer windings, furthest from the stator teeth 5. The surface of the wound stator coil 6 axial portion 8 that comprises the inner windings lies adjacent, for example in contact with, an axial portion 1 1 of a stator tooth 5. The wound stator coils 6 further comprise end portions 7 bending around the end portions 10 of the stator teeth 5 such as to interconnect the opposing axial portions 7 of the wound stator coil 6. The end portions 7 of the wound stator coil 6 is the bundle of current carrying wires interconnecting the axial portions 8 of the wound stator coil 6. The end portions 7 of the wound stator coil 6 comprises both inner windings closest to the stator tooth 5 and outer windings furthest away from the stator tooth. Figure 2 furthermore shows two cooling devices 1 a, 1 b mounted on the stator 3, for in use conducting heat from the plurality of wound stator coils 6 predominantly directly to the external heat sink 9. The cooling device 1 comprises an annular heat collector 12, i.e. a ring-shaped element. The annular heat collector 12 engages with the external heat sink 9,. Different embodiments for engaging the external heat sink 9 with the stator yoke 4 and with the annular heat collector 12 are shown in figures 5a-5d. The cooling device 1 comprises multiple coil receiving spaces 13 for receiving the end portions 7 of the wound stator coils 6. In particular, the cooling device 1 comprises one coil receiving space 13 per stator tooth 5, i.e. per wound stator coil 6 in an electrical machine 2 with concentrated windings. A coil receiving space is delimited by at least two radial extensions 14, 15 extending radially from the annular heat collector, a first radial extension 14 contacting outer windings of the end portions of the wound stator coil, and a second radial extension 15 contacting inner windings of the end portions of the wound stator coil. Each coil receiving space receives an end portion of a wound stator coil. The coil receiving spaces 13 divide the annular heat sink 12 into multiple circumferential sections with an equal arc of less than 360°. In certain embodiments, the multiple circumferential sections are separate components that are interconnectable such as to span the entire 360°. As will be explained below, the figures 7 and 8 show in detail one such circumferential section. Each one of the coil receiving spaces 13 is at least delimited by a rotor-facing surface 26 of the annular heat collector 12, a slotted tooth engaging radial extension 15 and a slotted coil engaging radial extension 14. The cooling device 1 , in particular the radial extensions 14, 15 and the annular heat collector 12, is made from a thermally conductive and non-ferromagnetic material, such that in use heat generated by the end portions 7 of the plurality of wound stator coils 6 is conducted in a radial direction along the plurality of radial extensions 14, 15 and along the annular heat collector 12 towards the external heat sink 9. The thermally conductive and non-ferromagnetic material is for example a Copper alloy or an Aluminum alloy.

Figures 3 and 4 show an exploded view of electrical machines 2 according to an embodiment of the present invention, wherein two exemplary embodiments of the cooling device 1 are displayed. The rotor, wound stator coils 6 and the external heat sink 9 are not shown for reasons of clarity. Figure 3 in particular shows the cooling device 1 wherein the annular heat collector 12 comprises separate interconnectable first 16 and second 17 annular parts. The first annular part 16 comprises an end surface, referred to as the stator facing surface 19 arranged to connect to an axial end surface of the stator yoke 4. When the first annular part 16 is mounted onto the stator 3, the stator facing surface 19 lies parallel and in contact with one of the axial end surfaces of the stator yoke 4. The first annular part 16 comprises the tooth engaging radial extensions or first radial extensions 15 arranged to contact the end portions 10 of the stator teeth 5. The first annular component 16 further comprises a plurality of slotted axial extensions 23 arranged to contact and cool axial portions 8 of the wound stator coils 6. The axial portions 8 of the wound stator coil 6 are positioned between the axial portions 1 1 of the stator teeth 5 and the axial extensions 23. The annular heat collector 12 is further provided with raised portions 22 extending throughout the first 16 and second 17 annular components. The surfaces of the raised portions 22 for example form side engaging radial extensions 27 further delimiting the coil receiving space 13. The second annular component 17 comprises the remainder of the annular heat collector 12, and thus comprises the end surface 20 opposing the stator facing surface 19 of the annular heat collector 12. The second annular component 17 also comprises second radial extensions, such as the coil engaging radial extensions 14, further delimiting the coil receiving spaces 13. The second annular component 17 further comprises a covering plate 21 integrally connected to the free end of each coil engaging radial extension 14. The covering plate 21 further delimits the coil receiving space 13 parallel to the rotor facing surface of the annular heat collector 12. In the embodiment shown in figure 3, the first annular component forms a main mounting unit which can be mounted to the stator 3 prior to the mounting of the wound stator coils 6 in wound state, i.e. as a pre-wound stator coil such as a form-wound winding or form-wound coil. After mounting the main mounting unit, the pre-wound stator coil 6 can be easily provided over the stator tooth 5 and the tooth engaging radial extensions 15. The second annular component 17 forms an auxiliary mounting unit. Due to the presence of the covering plate 21 , the pre-wound stator coil 6 can only be mounted, i.e. received in the coil receiving space 13, prior to mounting the auxiliary mounting unit on to the main mounting unit. Figure 4 shows the cooling device 1 wherein the annular heat collector 12 comprises integrally connected first 16 and second 17 annular parts. Furthermore, no covering plate 21 is provided in the embodiment in figure 4 as opposed to the embodiment shown in figure 3. Therefore, the first annular component 16 and second annular component 17 together form the main mounting unit. No auxiliary mounting unit is provided in this embodiment.

Figures 5a-5b show an inner-rotor electrical machine 2 according to an embodiment of the present invention wherein different external heat sinks 9 are provided. For reasons of clarity, the rotor and the wound stator coils 6 are not shown.

Figures 5c- 5d show an outer-rotor electrical machine 2 according to an embodiment of the present invention wherein different external heat sinks 9 are provided. For reasons of clarity, the rotor and the wound stator coils 6 are not shown.

In figures 5a and 5c the external heat sink 9 comprises a thermally conductive sleeve 9 in contact with the surface opposed to the rotor-facing surface. Preferably, the thermally conductive sleeve 9 has a thermal conductivity superior to the thermal conductivity of the stator core, i.e. the stator yoke 4 and the stator teeth 5. The surface opposed to the rotor-facing surface of the stator yoke 4, i.e. the radial surface of the stator yoke 4 not provided with stator teeth 5, and the surface opposed to the rotor-facing surface of the annular heat collector 12, i.e. the radial surface of the annular heat collector 12 not provided with first radial extensions such as the tooth engaging radial extensions 15, lie substantially flush when mounted. The external heat sink 9 comprises the thermally conductive sleeve 9 parallel to, and in contact, with both the surface opposed to the rotor-facing surface of the stator yoke 4 and the surface opposed to the rotor-facing surface of the annular heat collector 12.

In figures 5b and 5d the stator yoke 4 and the annular heat collector 12 comprise a set of openings 24 extending in the axial direction, and the external heat sink 9 comprises a plurality of cooling ducts formed by the set of openings 24, wherein the cooling ducts are arranged to in use extract heat from the stator yoke 4 and the annular heat collector 12 by flowing a heat transfer fluid through the cooling ducts. In the present embodiments the external heat sink 9 is a fluid jacket, for example a water jacket.

Figure 6 shows an cross-section of an electrical machine 2 according to an embodiment of the present invention wherein the cooling device 1 comprises multiple intermediate radial extensions 25. According to the present embodiment the multiple coil receiving spaces 13 of the cooling devices 1 are provided with further radial extensions, referred to as intermediate radial extensions 25, provided between the first radial extension, i.e. the stator tooth engaging radial extension 15 contacting the inner windings 18 of the end portions 7 of the wound stator coil, and the second radial extension, i.e. the coil engaging radial extension 14 contacting the outer windings 19 of the end portions of the wound stator coil. In the present embodiment, the windings of the wound stator coil 6, in particular the windings in the end portions 7 of the wound stator coil, are interspersed with the intermediate radial extensions 25 in the coil receiving space 13. The present embodiment enables to increase to contact between the windings in the end portions 7 of the wound stator coil 6 and the cooling device 1 such as to increase the cooling capabilities of the cooling device 1 .

Figures 7 shows in detail a single circumferential section of the cooling device 1 , for example of the cooling device 1 presented in figures 2 or 4. The coil receiving spaces 13 divide the cooling device 1 into multiple circumferential sections with an equal arc of less than 360°. Each one of the coil receiving spaces 13 is delimited by a rotor-facing surface 26 of the annular heat collector 12, at least 2 radial extensions, a first radial extension, for example a slotted tooth engaging radial extension 15 and a second radial extension, for example a slotted coil engaging radial extension 14. A pair of axial extensions 23 is connected to the annular heat collector 12.

Figure 8 shows a single circumferential section of the stator 3 comprising a stator tooth 5 that is mounted with a single wound stator coil 6, in particular comprising concentrated windings i.e. multiple turns of current carrying windings wound around the stator tooth 5. Figure 8 furthermore shows two circumferential sections of cooling devices 1 a, 1 b, as presented in figure 7, mounted on the stator 3. The end portions 7 of the wound stator coil 6 are received into the coil receiving spaces 13 of the cooling devices 1 a, 1 b.

Figure 9 shows a single circumferential section of the stator 3 comprising a stator tooth 5 that is mounted with a single wound stator coil 6, in particular comprising concentrated windings wound around the stator tooth 5. Figure 9 furthermore shows two circumferential sections of cooling devices mounted on the stator 3. The end portions 7 of the wound stator coil 6 are received into the coil receiving spaces 13 of the cooling devices. The cooling device comprises two parts. A first part of the cooling device comprises an annular heat collector 12 and axial extensions 23 integrally connected to the annular heat collector and extending (but not contacting) along the axial portions of the wound stator coil 6. The first part is made of non-ferromagnetic material, preferably a material with a very good thermal conductivity, such as for instance aluminum, ceramic materials or thermoplastic materials. A second part of the cooling device comprises an overmold or encapsulation piece providing an interface layer between the first part and the wound stator coil. The second part comprises the at least two radial extensions 14, 15 extending radially from the annular heat collector and forming a coil receiving space for receiving end portions of the wound stator coil between them. The overmold or encapsulation piece may be made from a non-ferromagnetic material with a good thermal conductivity. Preferably, the material also has good electrical insulating properties. This may reduce the need for adding electrical insulating sheets or liners between the cooling devices and the winding. Optionally, the overmold or encapsulation piece may also enclose the stator, i.e. the spaces between the windings and the stator tooth.

Claims

1 . A cooling device (1 ) for cooling an electrical machine (2), the electrical machine comprising wound stator coils (6), the wound stator coils (6) comprising end portions (7) and axial portions (8), the cooling device (1 ) arranged for in use conducting heat from the plurality of wound stator coils (6) to an external heat sink (9), the cooling device (1 ) comprising

• an annular heat collector (12) arranged for engaging with the external heat sink (9),

• a plurality of coil receiving spaces (13), each of the coil receiving spaces being delimited by at least two radial extensions (14, 15) each extending radially from the annular heat collector (12), the plurality of coil receiving spaces (13) being arranged for receiving end portions (7) of the plurality of wound stator coils (6),

wherein the cooling device (1 ) is made from a thermally conductive and non ferromagnetic material, such that in use heat generated by the plurality of wound stator coils (6) is conducted in a radial direction along the plurality of radial extensions (14, 15) and along the annular heat collector (12) towards the external heat sink (9).

2. A cooling device (1 ) according to the first claim, wherein the at least two radial extensions comprise a first radial extension (15) arranged for contacting inner windings of the end portions of the plurality of wound stator coils and a second radial extension (14) arranged for contacting outer windings of the end portions of the plurality of wound stator coils.

3. The cooling device (1 ) according to any one of the preceding claims, wherein the plurality of radial extensions (14, 15) are slotted in the radial direction.

4. The cooling device (1 ) according to any one of the preceding claims, wherein the annular heat collector (12) is divided into multiple circumferential sections each spanning an arc of less than 360°, wherein each circumferential section of the annular heat collector (12) is provided with a coil receiving space (13), and wherein the circumferential sections of the annular heat collector (12) are separate and interconnectable components.

5. The cooling device (1 ) according to any one of the preceding claims, wherein the cooling device (1 ) comprises a plurality of axial extensions (23), integrally connected to the annular heat collector (12), wherein the axial extensions (23) are arranged to contact the axial portions (8) of the wound stator coils (6).

6. The cooling device (1 ) according to the any one of the preceding claims, wherein the annular heat collector (12) comprises a first annular part (16) and a second annular part (17), and wherein the first annular part (16) and the second annular part (17) are separate and connectable parts.

7. The cooling device (1 ) according to any one of the preceding claims 1 - 5, wherein the annular heat collector (12) comprises a first annular part (16) and a second annular part (17), and wherein the first annular part (16) and the second annular part (17) are integrally connected parts.

8. An electrical machine (2) comprising

• a stator (3) having a stator yoke (4), a plurality of radially extending stator teeth (5) provided on the stator yoke (4), and a plurality of wound stator coils (6) comprising end portions (7) and axial portions (8),

• an external heat sink (9) engaging with the stator yoke (4) for removing heat from the electrical machine (2), and

• the cooling device (1 ) according to any one of the preceding claims, wherein the annular heat collector (12) engages with the external heat sink (9), and wherein the plurality of coil receiving spaces (13) receive end portions (7) of the plurality of wound stator coils (6), such that in use heat generated by the plurality of wound stator coils (6) is conducted in a radial direction along the plurality of radial extensions (14, 15) and along the annular heat collector (12) towards the external heat sink (9).

9. The electrical machine (2) according to the preceding claim, wherein

• the stator yoke (4) extends in an axial direction and wherein the stator yoke (4) is delimited by a radially inward surface, a radially outward surface and two axially opposed end surfaces each interconnecting the radially inward surface and the radially outward surface, • the plurality of radially extending stator teeth (5) are provided on a rotor-facing surface of the stator yoke (4), the rotor-facing surface being at least one of the radially inward surface or radially outward surface of the stator yoke (4), wherein the stator teeth (5) are delimited by opposing axial portions (1 1 ) and opposing end portions (10) each interconnecting the opposing axial portions (1 1 ),

• each wound stator coil (6) has opposing axial portions (8) extending along the opposing axial portions (1 1 ) of one of the stator teeth (5) and has opposing end portions (7) extending around the opposing end portions (10) of one of the stator teeth (5), and

• the annular heat collector (12) of the cooling device (1 ) is delimited by a radially inward surface, a radially outward surface and two axially opposed end surfaces (19, 20) each interconnecting the radially inward surface and the radially outward surface, and wherein the plurality of radially extending radial extensions (14, 15) are provided on a rotor-facing surface (26) of the annular heat collector (12), the rotor-facing surface (26) being at least one of the radially inward surface or radially outward surface of the annular heat collector (12),

• wherein the cooling device (1 ) is mounted on the stator (3) such that one of the end surfaces (19) of the annular heat collector (12), called the stator facing surface (19), lies parallel with, and adjacent to, one of the end surfaces of the stator yoke, and preferably wherein the stator facing surface (19) of the annular heat collector (12) is in contact with one of the end surfaces of the stator yoke (4).

10. The electrical machine (2) according to the preceding claim, wherein the plurality of radially extending stator teeth (5) are extending respectively radially outward from the outer radial surface of the stator yoke (4) or radially inward from the inner radial surface of the stator yoke (4), such as to form respectively an outer-rotor electrical machine or an inner-rotor electrical machine, and wherein the plurality of radial extensions (14, 15) are extending respectively radially outward from the outer radial surface of the annular heat collector (12) or radially inward from the radially inward surface of the annular heat collector (12).

1 1 . The electrical machine (2) according to any one of the preceding claims 9 - 10, wherein the surface opposed to the rotor-facing surface of the stator yoke (4) and the surface opposed to the rotor-facing surface of the annular heat collector (12) lie substantially flush, and wherein the external heat sink (9) comprises a thermally conductive sleeve in contact with both the surface opposed to the rotor-facing surface of the stator yoke (4) and the surface opposed to the rotor-facing surface of the annular heat collector (12).

12. The electrical machine (2) according to any one of the preceding claims 9-1 1 , wherein each coil receiving space (13) is further delimited by the rotor facing surface (26) of the annular heat collector (12).

13. The electrical machine (2) according to the any one of the preceding claims 9-12 in combination with any one of the preceding claims 6-7, wherein the first annular part (16) comprises the stator facing surface (19) and wherein the second annular part (17) comprises the end surface (20) of the annular heat collector (12) opposing the stator facing surface (19).

14. The electrical machine (2) according to any one of the preceding claims 9-13, wherein the first radial extension (15) delimiting each coil receiving space (13) is a tooth engaging radial extension (15) extending radially from the rotor-facing surface (26) of the annular heat collector (12) adjacent the stator facing surface (19) of the annular heat collector (12), towards a free end, the tooth engaging radial extension (15) being delimited by a tooth engaging surface, an opposite coil engaging surface and two sidewalls each interconnecting the tooth engaging surface and the coil engaging surface, the tooth engaging radial extension (15) simultaneously contacting one of the end portions (10) of the stator tooth (5) with the tooth engaging surface and one of the corresponding end portions (7) of the wound stator coil (6) with the coil engaging surface.

15. The electrical machine (2) according to any one of the preceding claims 9-14, wherein the second radial extension (14) delimiting each coil receiving space (13), is a coil engaging radial extension (14) extending radially from the rotor-facing surface (26) of the annular heat collector (12) adjacent the end surface (20) opposite to the stator facing surface (19) of the annular heat collector (12), towards a free end, the coil engaging radial extension (14) being delimited by a coil engaging surface in contact with one of the end portions (7) of the wound stator coil (6).

16. The electrical machine (2) according to any one of the preceding claims 8-15 in combination with claim 13, wherein the cooling device (1 ) comprises a main mounting unit comprising at least the first annular part (16) of the annular heat collector (12), wherein the main mounting unit is arranged to enable mounting of the wound stator coil (6) in wound state on to the stator tooth (5) after mounting of the main mounting unit on to the stator (3).

17. The electrical machine (2) according to the preceding claim, wherein the cooling device (1 ) comprises a further mounting unit, called the auxiliary mounting unit, the auxiliary mounting unit comprising a covering plate (21 ) extending axially substantially parallel to the rotor-facing surface (26) of the annular heat collector (12), wherein the covering plate (21 ) is delimited by a coil engaging surface arranged to contact one of the end portions (7) of the wound stator coil (6), wherein each coil receiving space (13) is further delimited by the covering plate (21 ), wherein the auxiliary mounting unit is mountable to the main mounting unit, and wherein the wound stator coil (6) in wound state is only mountable on to the stator tooth (5) prior to connecting the auxiliary mounting unit with the main mounting unit.